The invention pertains to vertebral body fusion. Specifically, the invention is directed to instrumentation and methods for insertion of spinal implants between opposing vertebral bodies to facilitate fusion of the bodies.
Chronic neck and back problems can cause pain and disability for a large segment of the population. Frequently, the cause of the pain is traceable to diseased disc material between opposing vertebrae. When the disc material is diseased, the opposing vertebrae may be inadequately supported, resulting in persistent pain.
Surgical devices and techniques have been developed for removing diseased disc material and fusing the joint between opposing vertebral bodies. Arthrodesis of the intervertebral joint can reduce the pain associated with movement of a joint having diseased disc material. Some fusion techniques involve removal of the diseased disc, drilling a bore for receiving a fusion implant into the bore and inserting the implant between the opposing vertebral bodies.
Spinal fusion implants and related surgical instruments for implanting a fusion device are known and disclosed in, for example, U.S. Pat. Nos. 5,741,253; 5,658,337; 5,609,636; 5,505,732; 5,489,308; 5,489,307; 5,484,437; 5,458,638; 5,055,104; 5,026,373; 5,015,247; and 4,961,740, the disclosures of which are incorporated herein by reference.
Procedures for fusing an intervertebral joint space include removing disc material and preparing a bore for placement of one or more implants in the disc space by removing bone from opposing vertebrae which are adjacent to the disc space. Currently two of the most common approaches for preparing the bore are free-hand preparation using a powered boring device and manual or powered boring through a hollow guide tube. Systems which provide for preparing the implant site bore through a hollow guide tube are described in, for example, U.S. Pat. Nos. 5,484,437 and 5,489,307. Preparing the implant site by passing instruments, such as reamers or taps, through a hollow guide tube advantageously provides an isolated surgical field with reduced chance of injury to tissues surrounding the surgical site.
However, free-hand preparation of the implant site and some of the available hollow guide tube systems often do not provide a means for ensuring that an equal amount of bone is removed from the adjacent vertebral bodies during formation of the bore. This is particularly true for current systems used to fuse cervical vertebrae. In addition to other problems, removal of unequal amounts of bone can result in over reaming of one vertebra relative to the adjacent vertebra. Also, free-hand preparation and most hollow tube systems do not adequately ensure that reaming of the bore is performed parallel to the vertebral endplates. Failure to ream parallel to the endplates and/or over reaming of the vertebral bodies can result in misplacement of the fusion device or subsidence of the joint space post operatively.
Moreover, many of the available hollow tubes presently used as guides are relatively long, some having lengths that can be 10 to 30 times greater than the diameter of the bore. This length obscures direct visualization of the surgical site and prevents the surgeon from being able to continuously monitor, and adjust as needed, during the reaming or tapping procedure. In addition, while some presently available hollow tubes include paddles for insertion into the disc space, the paddles typically are short relative to the length of the hollow tube (e.g., having a paddle length:tube length ratio of about 1:6 to 1:35). Long hollow tubes relative to short paddles can introduce a significant lever arm effect. In such arrangements, small movements at the proximal end of the hollow tube can significantly alter the trajectory of a reamer or other instruments guided by the hollow tube. In addition to hollow instrument guides, the precision and ease of use of the instruments which are passed through the guide can also affect surgical outcome.
Thus, there is a continuing need for greater precision, safety and ease of use of instrumentation used for placement of spinal fusion implants. The present invention is directed to addressing these needs.
The present invention is directed to increasing the ease and enhancing the precision of placement of spinal fusion implants between opposing vertebral bodies. In particular, the invention provides instruments and methods for performing a spinal surgical procedure through a hollow guide wherein the guide has a low lever arm effect and can provide greater visibility when the guide is placed over a surgical site.
The invention also provides novel instrument guides, implant gauges, guide starters, reamers, taps and other associated instruments which can be used alone or combined in a kit to perform a spinal surgical procedure. The principles underlying some of the adjustable features of the instruments of the invention may also be advantageously applied for use with prior art hollow guide systems.
Methods for implanting a spinal implant into a disc space between opposing vertebral bodies using instruments and kits of the invention are also disclosed.